Microarrays are important tools for diagnostic applications in research and clinical settings. A major process in the fabrication of microarrays is the patterning of biomolecules such as proteins and DNA onto a solid support in a controlled fashion. In traditional microarrays, biomolecules such as proteins and DNA are introduced directly onto a solid substrate surface using spotting technology. However, the poor precision and low reproducibility of spotting technology results in the production of microarrays with numerous inaccuracies.
On the other hand, bead microarrays carry microbeads which in turn are conjugated to biomolecules. Bead microarrays have significant advantages over traditional spotted microarrays, such as consistency, flexibility and faster kinetics. Bead microarrays offer greater flexibility because the surface chemistry of the beads can be tailored to suit the biomolecule to be conjugated on the bead. Potentially, any type of microarray such as drug-, metabolite-, lipid- or carbohydrate-microarrays can be manufactured by using beads. Further, bead microarrays ensure consistent results since the dimensions of the beads can be made identical.
However, one of the main problems with bead microarrays is the encoding and decoding of individual beads to determine the identity of the bead and the type of molecule the bead carries.
Currently, bead arrays typically come in the form of “liquid arrays” or “planar arrays”. In liquid arrays, beads remain in suspension and are read out and decoded via a physical signature, e.g. a color tag, during flow cytometer based analysis, such as VERACODE assays of ILLUMINA INC., San Diego, Calif., United States of America and XMAP referencing of LUMINEX CORPORATION of Austin, Tex., United States of America.
In planar arrays, beads are deposited onto a substrate material and typically identified by a physical signature, e.g. color tags, oligonucleotide sequences, bead shape and size or other means. The array is analyzed by taking a picture, typically with a microscope or microarray scanner.